"FIRST THEY CAME", a poem

“First they came…” is a famous statement attributed to pastor Martin Niemöller (1892–1984). To me, it describes simply but very effectively how good individuals become progressively corrupted by their lack of empathy, and thus how easily a nation descends into totalitarian rule. 
There are a few versions of the statement, go ahead and substitute the subjects as you see fit. The following version captures Niemöller's point:

First they came for the socialists,

and I didn't speak out because I wasn't a socialist.

Then they came for the trade unionists,

and I didn't speak out because I wasn't a trade unionist.

Then they came for the Jews,

and I didn't speak out because I wasn't a Jew.

Then they came for me,

and there was no one left to speak for me.

Related to this idea, someone else said (I paraphrase): 
all that evil needs in order to win, is for people of good will do nothing.